When you download the D2 LoD from the download site, it downloads version 1.14B of the game. To use Battle.Net, you need version 1.14D.
See my post under for instructions on how to upgrade:
Also, this forum here is for issues on the Battle.Net desktop app; for issues on Diablo II (2000) and/or Diablo II: Lord of Destruction, you should be using the Classic Games Tech Support forum: